The present invention relates, in general to fluid sealing means disposed about the rotor of a gas-cooled dynamoelectric machine used to prevent axial leakage of gas coolant out of each end of the dynamoelectric machine along the rotor surface. The sealing means must provide a gas-tight seal and yet maintain a radial mobility upon the occurrence of a rotor-seal rub.
U.S. Pat. No. 2,647,771 to Grobel issued Aug. 4, 1953 gives a general description of the environment for which the present invention is intended. More particularly, the sealing means to which the present invention may be most advantageously applied comprises a pair of sealing rings which are resiliently mounted in an annular holder at each end of the dynamoelectric machine. The sealing means comprises a gas side sealing ring and an air side sealing ring which are axially spaced apart within each holder to define an oil feed annulus therebetween. The oil feed annulus is connected to a source of pressurized oil which distributes oil through the oil feed annulus to an annular gap between the radially inner surfaces of the rings and the surface of the rotor. The seal oil pressure is from 5 to 8 psi higher than the gas coolant pressure and hence the oil prevents the axial leakage of gas coolant out along the ends of the machine.
It may be desirable to increase the gas coolant pressure within the dynamoelectric machine in order to increase the cooling capacity of the machine. If the coolant gas pressure is increased, then the seal oil pressure must be proportionately increased in order not to destroy the effectiveness of the seal. The increase in seal oil pressure on the gas side ring makes little difference since the pressure increases on both sides of the gas side ring are substantially equal and hence the net axial force on the gas side ring remains the same. On the other hand, an increase in seal oil pressure on the air side ring (adjacent ambient pressure) results in an increase of the net force on the air side ring which, in effect, jams the ring against the annular holder causing a loss in radial mobility. In the event the rotor contacts the air side sealing ring and it is not free to move radially, the sealing ring or rotor could be permanently damaged.
It is therefore one object of the present invention to provide a rotor (shaft) seal at each end of a dynamoelectric machine which will retain radial mobility as machine gas pressures increase.
It is another object of the present invention to provide a rotor (shaft) seal at each end of a dynamoelectric machine having a means available for balancing seal oil pressure increases against the air side seal.
The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof, may best be understood with reference to the following description taken in conjunction with the drawing.